1. Technical Field
The present invention relates to an electroluminescence device, an electronic equipment and manufacturing methods thereof.
2. Related Art
Generally, an organic electroluminescence element, which is hereinafter referred to as the “organic EL element” and which composes the organic electroluminescence device, includes, for example, a first electrode or a positive electrode and a second electrode or a negative electrode, between which an organic luminescent material is laminated. Electrons and holes charged from the above stated both electrodes recombine within the luminescent layer to allow the excited energy to be discharged in the form of light emission.
In such an organic EL device, it is material to pay an attention to a possible existence of a charge injection barrier between each electrode and a luminescent layer. Tang et al. teach to utilize magnesium (Mg) having small work function in order to lower an energy barrier which disturbs an injection of electrons from the negative electrode. A technical literature Appl. Phys. Lett., 51,913 (1987) is an example of related art. In the technical literature, since Mg is apt to be oxidized and unstable in the atmosphere, Mg is alloyed by coevaporation with Ag which is relatively stable. Alternatively, calcium (Ca) is often used for the reason of the small work function. Here, a covering film made of aluminum (Al) or the like is employed as a protection layer.
Another examples of related art are L. S. Hung, C. W. Tang, and M. G. Mason, Appl. Phys. Lett. 70,152 (1997) and JP-A-09-17574. Those examples of related art report that a thin film made of alkali metal such as LiF and MgO or halogenized or oxidized alkali earth metal is inserted between the negative electrode and the organic layer in order to produce a high efficiency.
Further example of related art is JP-A-11-162646. This example of related art reports that use of a metal complex of the alkali metal or the alkali earth metal in the form of the electron injection layer will provide the organic EL element having a high light emission efficiency.
When a chemical compound of the alkali metal or the like having low work function is inserted to serve as the electron injection layer between the organic layer and the negative electrode, it is said that a factor which produces the effect of the high efficiency is a reducing reaction or a vacuum level shift upon deposition of the negative electrode. With regard to the reducing reaction, it is considered that, since an attempt of enhancement of the characteristic resembles to an attempt of the work function of the metal composing the chemical compound, a metallic compound is reduced to a status of metal upon deposition of the negative electrode such as Al, thereby improving the electron injection characteristic.